The tabs layout does not show articles under the main top categories, those categories are assigned as tabs for layout purposes, you need to assign them to the subcategories within each tab category. In your KB Overview page it should be showing you warning messages explaining what you need to do.

If you experiencing with issues like new articles are not being displayed or category name changing doesn’t show the new name. This is usually caused by aggressive caching. To see if that is the issue, try disabling your caching plugin or your server caching, then refresh your browser cache. Then test the issue, if it’s resolved you will need to exclude the main page from your caching or refresh your cache to see your new changes.